Commonly, a conventional shredding cutter and its machining process include three types as following.
First, a fixed way with spacing rings. As shown in FIGS. 1(a)-1(c), the cutter includes a cutter shaft 11, blades 12, spring retainers and spacing rings 14, wherein each blade 12 is fixed on the cutter shaft 11 between the adjacent spacing rings 14, and the cutter shaft 11 are fixed by two spring retainers retaining the cutter shaft 11 at opposite ends respectively. The advantages of this machining method of the cutter are that the process is simple and the operation is convenient. However, its disadvantages includes that (a) the cost of the total cutter is increased as the spacing rings are needed; (b) the assembly difficulty is increased since the spacing rings and the blades are superimposed each other, and both of them have thickness tolerances, the small tolerances are finally cumulated to cause the spring retainers may not be assembled; (c) the spacing rings are easy to get broken since it can only stand a limited force.
Second, a machining way with a ball bearing expansion hollow tube. As shown in FIGS. 2(a)-2(c), this cutter includes a cutter shaft 21 and a plurality of blades 22, wherein the cutter shaft 21 is a hollow steel tube. During the machining process, a ball bearing 23 (a steel ball) rolls in the cutter shaft 21, and the cutter shaft 21 is expanded as the diameter of the ball bearing 23 is slightly larger than the inner diameter of the cutter shaft 21, thereby the blades 22 are fixed on the cutter shaft 21. The advantages of this machining method of the cutter are that the cost is reduced as the spacing rings are needless, and the operation is convenient. However, its disadvantages include that (a) the cutter shaft can not stand a great torsion of the blades (compared to the polyhedral solid cutter shaft) since the cutter shaft is a hollow tube structure; (b) since the cutter shaft is a hollow tube structure as mentioned, thus the pressure it can stand is smaller than that of the solid cutter shaft. During the operation of the cutter shaft, the cutter shaft is easy to distort once a greater pressure is stood, which is only applicable to a small quantity of paper therefore.
Third, a unitary machining way. The machining way does a turning to a solid bar to form a unitary cutter. The advantages of this machining method of the cutter are that the structure is unitary with a reliable intensity. However, its disadvantages are that (a) requirements of the turning process are quite high, the turning quantity is large, and the yield is low; (b) numbers of mechanical processing equipments are needed in the mass production, the rate of the quality products is low, and the reparability is small.